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  #1  
Old 12-29-2012, 04:00 PM
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Dave Bernard Dave Bernard is offline
 
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Default Ugly Fuel Tank Screw Countersink on main spar

Using the Vans method of #30 Countersink using a platenut as a guide, it sure didn't come out too pretty:



Pretty disappointed as from here on the mistakes start getting expensive! Anticipating me screwing this up, I only riveted one platenut on to try this method. Did about 5 hours of research about this hole prior to cutting it- High anxiety!

Since this is just a hole for a dimple, should I switch to the other method (backing bar w rivets and #30 guide hole) or do the hole just come out like this sometimes?
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  #2  
Old 12-29-2012, 04:12 PM
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Dave it does happen some times, but technique is a big factor.

Do not use an air drill.
Do not turn the cutter fast.

Use a good cordless drill with good torque.
Make sure the countersink cage is set up properly by testing on scrap and to practice your technique.

Use a lot of pressure and slow speed (not ultra slow... you will learn with practice). If the drill has selectable speeds, use one of the slower ranges so that you can run the motor at full.

The slower speed with a lot of pressure will minimize the likelihood of cutter chatter.
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Old 12-29-2012, 04:20 PM
N427EF N427EF is offline
 
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Everything Scott said.
I found the single flute countersink tools from Clevland Tools very helpful for some applications, especially the ones you are working on.
http://www.cleavelandtool.com/prodinfo.asp?number=CCSF
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Old 12-29-2012, 04:22 PM
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A one-hole countersink cutter would help here, again at a low speed...

http://www.aircraft-tool.com/shop/de...UCT_ID=4100-30

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Old 12-29-2012, 04:32 PM
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And don't forget the Boelube.
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Old 12-29-2012, 04:44 PM
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Heck with the nutplate method... grab a piece of .060 or heck even 1/8" bar stock and drill it up with the correct drill size. Use the rivet holes for a neighboring nutplate to drill and cleco the piece on the back side and then Countersink the spar. You will have a few different patterns... Check and set the plate up for each hole. The countersink will be clean and smooth... oh and very hard to make the countersink chatter. You will be extremely pleased.
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Last edited by LifeofReiley : 12-29-2012 at 04:53 PM.
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Old 12-29-2012, 04:50 PM
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What Riley said. A good thick piece of metal on the back side to hole the guide in the countersink will prevent this from happening. If you look at the hole in your countersink, the hole is enlarged so nothing holds the guide point anymore.
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Old 12-29-2012, 05:10 PM
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As always, there are a lot of different ways to complete a process... some take a lot more time and effort than the one described in the manual, which does work well, if the proper technique is used (and some lubricant that I forgot to mention... thanks Walt).
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Old 12-29-2012, 05:50 PM
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Quote:
Originally Posted by CharlieWaffles View Post
What Riley said. A good thick piece of metal on the back side to hole the guide in the countersink will prevent this from happening. If you look at the hole in your countersink, the hole is enlarged so nothing holds the guide point anymore.
Mark is correct, using the nutplate method your nice facory hole will end up way oversized. For me it is all about quality and sometimes it can take a little more time but the end product is well worth it.
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Old 12-29-2012, 06:13 PM
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Quote:
Originally Posted by LifeofReiley View Post
Mark is correct, using the nutplate method your nice facory hole will end up way oversized. For me it is all about quality and sometimes it can take a little more time but the end product is well worth it.
I disagree...
I have at least 10 sets of wings using the described method (install the nut plate first, and use the proper size pilot, and turn it slow).
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